The present invention relates generally to optical imager manufacturing and, more particularly, to a method and apparatus for testing imager devices using a center turning optic.
There are a number of different types of semiconductor-based imagers, including charge coupled devices (CCDs), photo diode arrays, charge injection devices and hybrid focal plane arrays. CCDs are often employed for image acquisition for small size imaging applications. CCDs are also capable of large formats with small pixel size and they employ low noise charge domain processing techniques. However, CCD imagers have a number of disadvantages. For example, they are susceptible to radiation damage, they exhibit destructive read out over time, they require good light shielding to avoid image smear and they have a high power dissipation for large arrays.
Because of the inherent limitations in CCD technology, there is an interest in complementary metal oxide semiconductor (CMOS) imagers for use as low cost imaging devices. A fully compatible CMOS sensor technology enabling a higher level of integration of an image array with associated processing circuits is beneficial to many digital applications such as, for example, in cameras, scanners, machine vision systems, vehicle navigation systems, video telephones, computer input devices, surveillance systems, auto focus systems, star trackers, motion detection systems, image stabilization systems, and data compression systems for high-definition television.
After an imager has been manufactured, a test apparatus is used to verify the proper functionality of the imager. A light source in the test apparatus provides collimated light that is directed over imager devices that are mounted to a test circuit board. The imager devices may be in the form of packed or unpackaged die, depending on the point in the production flow at which they are functionally tested. When the imager devices are illuminated by the light source, the test circuit board runs one or more test procedures that operate the imager devices to capture the image provided by the light source and determine if the capture was accurate.
Conventional light sources are sized to illuminate multiple imager devices in parallel. Such parallel testing is limited by the effective area that a light source can produce consistent, uniform light to the devices as well as how closely the devices can be mechanically mounted to the test circuit board. Currently available test apparatus allow parallel testing of about four imager devices using a light source capable of producing collimated light over an approximately 38 mm diameter region. Increasing the size of the light source to cover an approximately 77 mm diameter region to allow parallel testing of eight imager devices would result in an extremely costly test apparatus. For example, a single light source for such an apparatus is estimated to cost over $100,000.
Due to the constraints of the light source the number of imager devices that can be tested in parallel is limited. Each set of four devices tested must be unloaded and a new set of devices must be mounted to the test circuit board between tests. Hence, the time required to test a group of devices is significant.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the present invention described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.